Conventionally, in a case where heat is used as energy for domestic and industrial uses, the use of a thermal storage body, i.e., a medium for thermal transportation and temporary storage, has been proposed when the heat is generated and consumed at different places, and when there is a time lag between the generation of heat and the consumption thereof.
Thermal storage bodies typically exploit either sensible heat taking advantage of the thermal capacity thereof or latent heat produced by a transformation of phase thereof. Latent heat is a phenomenon of heat absorption upon the transformation from solid phase to liquid phase and heat release upon the transformation from liquid phase to solid phase.
Examples of such thermal storage bodies taking advantage of sensible heat include water, stone, and various kinds of metals. However, those taking advantage of sensible heat have drawbacks: a larger thermal storage tank is required to compensate for the low thermal capacity thereof and the low specific latent heat thereof, and the temperatures at the heat source and at the heat consumption are restricted because of a possible wide temperature range upon the extraction of the heat.
Meanwhile, examples of such thermal storage bodies taking advantage of latent heat include inorganic hydrated salts and hydrocarbons such as paraffins. However, it is known that inorganic hydrated salts generally show great supercooling, which results in serious drawbacks for real use: namely, freezing is hindered even below the melting point, and specific heat released is substantially reduced.
For these reasons, researches have been widely conducted to develop thermal storage agents from oil-soluble substances (oily substances) composed of paraffins and other hydrocarbons. Among them, oil-soluble substances such as paraffins and higher alcohols are attracting a large attention, because they release as comparatively large a amount of melting latent heat as approximately 40 cal/g to 60 cal/g, exceeding 30 cal/g, by a transformation from solid phase to liquid phase and vice versa, and also because they can offer any melting point ranging from as low as -20.degree. C. to as high as 100.degree. C. depending on the kind and/or mixture thereof.
The oil-soluble substances have disadvantages too: Since most of the oil-soluble substances are inflammable, when in liquid phase, they may leak, catch fire and spread easily. And paraffins and other hydrocarbons, when left at high temperatures for a long period of time, deteriorate in physical property and show supercooling, which causes serious negative effects.
To solve the disadvantage of the deterioration in physical property and the resultant supercooling, which causes serious negative effects, of paraffins and other hydrocarbons when left at high temperatures for a long period of time, it has been suggested to prevent supercooling by adding a nucleating agent (core forming agent) such as zeolite particles to paraffins and other hydrocarbons. However, such a nucleating agent still fails to produce enough of the potential effects thereof with hydrocarbons, because the nucleating agent is separated during use, especially when the hydrocarbons are in liquid phase, from the hydrocarbons in liquid phase due to the difference in specific weight.
When such hydrocarbons including paraffins are used as thermal storage agents for storing latent heat, since the hydrocarbons are used indoors in a large quantity, some preventive measures should be taken against the leakage thereof from the container due to the flow thereof when liquidized, so as to bring the thermal storage agents in line with Fire Service Law and other regulations over the use of inflammable thermal storage agents.
Accordingly, solutions to the aforementioned problems are suggested. Some of the examples are:
1 a thermal storage material of a paraffin gelled by a gelling agent such as an amide, ester, or amino salt of N-acyl amino acid, or 12-hydroxy stearic acid (Japanese Laid-Open Patent Application No. 56-103273/1981 (Tokukaisho 56-103273)),
2 a thermal storage body prepared by filling a bag-like sealed container with foaming substance holding a mixture of a paraffin and di-benzylidene sorbitol like an isolated island (Japanese Laid-Open Patent Application No. 57-96078/1982 (Tokukaisho 57-96078)),
3 a latent thermal storage device using a paraffin that is gelled like jelly by a freezing agent and sealed in a capsule (Japanese Laid-Open Patent Application No. 6-58686/1994 (Tokukaihei 6-58686)),
4 a thermal storage material prepared by mixing a paraffin and a hydrocarbon organic high polymer by mechanical means (Japanese Laid-Open Patent Application No. 4-85387/1992 (Tokukaihei 4-85387)) (The mixing with mechanical means refers to operations to stir, mix and knead in a state where any component to be mixed can flow or be deformed by an external force due to high temperatures or due to swelling, or preferably solution, of at least one of the components, i.e., a paraffin or a hydrocarbon organic high polymer, in a melted product of the other component.),
5 a thermal storage material prepared by diffusing oil absorbent resin particles having absorbed a paraffin in water, brine, etc. (Japanese Laid-Open Patent Application No. 6-116550/1994 (Tokukaihei 6-116550)),
6 a thermal storage device made up of a thermal storage tank filled with tiny solid oil absorbent resin particles having absorbed a paraffin so that the tiny particles can exchange heat with a thermal storage body such as water (Japanese Laid-Open Patent Application No. 4-278186/1992 (Tokukaihei 4-278186)), and
7 a thermal storage agent prepared by impregnating, with a paraffin, pellets made of a polyolefin such as polyethylene (Japanese Laid-Open Patent Application No. 62-277484/1987 (Tokukaisho 62-277484) and Japanese Laid-Open Patent Application No. 2-170887/1990 (Tokukaihei 2-170887)).
However, the thermal storage agents disclosed in Patent Applications 1 to 4 may be dangerous: Paraffin may seep and is fluidized in a large quantity as a result of repeated transformations of phase (freezing and melting). If the container or capsule is broken, paraffin may leak, catch fire and spread.
The thermal storage agent and device disclosed in Patent Applications 5 and 6 have drawbacks: They are arranged so that the paraffin absorbed in an oil absorbent resin is dispersed in a medium such as water in minuscule volume units. The thermal storage agent and device with such an arrangement do not freeze at a target temperature or within a predetermined time, and the heat stored by heating or cooling cannot be extracted efficiently, i.e., a satisfactory thermal storage efficiency cannot be obtained.
Meanwhile, the thermal storage agent disclosed in Patent Applications 7 has a disadvantage of latent heat of a low quantity, because the equilibrium absorption ratio is low with respect to the paraffin present in polyolefin as an oil absorbent resin. In addition, in order to prevent the paraffin from seeping from the thermal storage agent, it is necessary to coat or crosslink the surface of the polyethylene, etc., to increase the viscosity of the paraffin, and to carry out the process of paraffin absorption at high temperatures.
In the above Patent Applications, since the thermal storage material is a molded product either gelled or mixed with a binder component in advance, it is troublesome to fill, with the thermal storage body as a molded product, such a container having a complex shape to ensure a large contact area with a medium, for example, a container having a shape of a small tube, donut, coil, etc. Besides, it is difficult to completely fill up the container with the molded product, and a resultant low filling ratio leads to a low thermal efficiency.
Moreover, when the container is filled with the thermal storage material prepared by a method disclosed in Patent Application 1, the filling operation needs to be conducted at very high temperatures such that the thermal storage material is melted and liquidized. Therefore, practically, the thermal storage material cannot be used to fill a container of a low thermal resistance, such as a container fabricated from polyvinyl chloride, and can only be used with, for example, a container fabricated from a highly heat resistant, but, expensive resin material or a corrosion resistant, but, expensive stainless steel.
The present invention, in view of the above yet-to-be-solved problems and disadvantages, has an object to provide a highly safe thermal storage agent with a good thermal storage efficiency and a manufacturing method of such a thermal storage agent, and to further provide a thermal storage device, a thermal storage material, and a manufacturing method thereof.